The majority of copper stripping sold in garden
shops for this purpose is not wide enough to create an effective barrier,
which would need to be six inches wide, or the largest most destructive
slugs will hump right over it without touching the copper.

Six inch copper? Good Lord, what kind of slugs are we having here? Something
big enough to "hump" over that is big enough to eat! Maybe a night watchman
with a shotgun is required. (is there a hunting season?)
Old Chief Lynn